Temperature dependence of a femtosecond degenerate four-wave mixing signal from 350-µm-thick undoped InP far below the band gap

We experimentally investigated the temporal and spectral profiles of the four-wave mixing (FWM) signals from 350-µm-thick undoped InP at various temperatures when the laser was tuned from the exciton resonance to 100 meV below the band gap. The temporal and spectral shapes of the observed FWM signals well below the band gap were nearly consistent with those of the excitation laser pulse and exhibited significantly different behavior from the excitonic properties in thin samples. Furthermore, we observed temperature-independent large blue shifts of the spectrally resolved FWM signals far below the band gap with respect to the excitation laser spectrum when the time delay moved from positive to negative. Based on our experimental observations, we conclude that this behavior can be explained not simply by the excitonic effects but by the instantaneously created virtual states and the frequency-broadening effect.